In materials processing with high power lasers, scanner devices are increasingly being used for the rapid positioning of the laser beam. As long as the beam deflection is performed with scanner mirrors in the (very nearly) collimated beam, for focusing a so-called f/theta lens system is used, which is characterized in particular by a large, planar image field. In the range up to about 1 kW average laser power, such f/theta lens systems are normally assembled from approximately six spherical lenses made from different and also highly refractive glasses. These lens systems are typically optimized for marking applications, i.e. these lens systems have a very high (almost diffraction-limited) imaging quality, but only a moderate power tolerance. In the range above 100-200 W average laser power, a marked shift of focus and a thermally conditioned degradation of the imaging quality typically occur. Above around 1 kW average laser power, the f/theta lens systems in current use can only be used for materials processing either in a very limited way or not at all, since marked deficits in the ability of the radiation to be focused and damage due to overheating of the lenses occur. Alternatively, beam guiding systems with beam deflection in the focused beam are used in scanner devices, in which the requirements on the lens system are lower. In any case, the usable working distance is considerably reduced by the scanner mirrors. In this case, the image field is severely spherically distorted, which is normally compensated by a z-adjustment of the lens. At large working distances—depending on the numerical aperture of the focused beam—the scanner mirrors required are very large, which restricts their dynamic behavior. From U.S. Pat. No. 6,396,616, a laser imaging system is known, the laser imaging system having a scanner mirror and an f/theta lens system with a spherical, an aspherical, and a toroidal lens, which acts as a reducing lens to increase the optical beam power.